Policy-Enabled Hando s Across Heterogeneous Wireless Networks

\Access is the killer app" [3] is the vision of the Daedalus project at U.C. Berkeley. Being able to be connected seamlessly anytime anywhere to the best network still remains an unful lled goal. Often, even determining the \best" network is a challenging task because of the widespread deployment of overlapping wireless networks. In this report, we describe a policy-enabled hando system that allows users to express policies on what is the \best" wireless system at any moment, and make tradeo s among network characteristics and dynamics such as cost, performance and power consumption. We designed a performance reporting scheme estimating current network conditions, which serves as input to the policy speci cation. A primary goal of this work is to make it possible to balance the bandwidth load across networks with comparable performance. We identi ed the problem of hando instability that may be caused by hando synchronization, i.e., the scenario of many mobile hosts making the same hando decision at essentially the same time. We use randomization to break such synchronizations. Given the current \best" network, our system also determines whether the hando is worthwhile based on the hando overhead and potential network usage duration.